The only thing you can do is to make sure that the battery supply is staying
level when the light is working. It is also possible that this device is
very cheaply designed, and there was not proper consideration for the
magnetic field that the light wiring would be causing when there is current
flow through it.

I would have no idea in something like the device that you have, where you
can have effective magnetic shielding. If you start with magnetic shielding,
I am very sure you will have problems to take readings with it.

I have used electronic compasses that are very high end. They have
incorporated in to their design, compensation for the internal electrical
operation.

--

Jerry G.
======


"Roy Hammond" wrote in message
...
Recently I purchased a new fluxgate compass (trademarked Williams F1 made
in China) very neat, and cheap (£9.99). It works fine and calibrates well,
but when the LCD blue glow backlight button is pressed, it lights-up for
the requisite 60 seconds or so, BUT the compass reading goes all over the
place - quite unusable! I guess that was why the compasses were selling so
cheaply in the store. Only for use in daylight!
The backlight is electrolumninescent and obviously is generating a
spurious magnetic field. Has anybody any experience or ideas on how this
problem can be overcome?
-Roy-
(Surrey, England)